E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.

Hecatomb.

It is said that Pythagoras offered up 100 oxen to the gods when he discovered that the square of the hypothenuse of a right-angled-triangle equals both the squares of the other two sides. This is the 47th of book i. of “Euclid,” called the dulcarnein (q.v.). But Pythagoras never
sacrificed animals, and would not suffer his disciples to do so.

1

“He sacrificed to the gods millet and honeycomb, but not animals. [Again] He forbade his disciples to sacrifice oxen.”—Iamblichus: Life of Pythagoras, xviii. pp. 108–9.